Landfilling, the traditional disposal route, is still the cheapest option, but sites are becoming scarcer, and disposal costs are mounting as environmental protection standards are raised. Sanitary land-fill or controlled tipping is an acceptable method in suitable locations, if the possibility of pollution of surface water and ground water is eliminated. In some cases refuse is mechanically reduced in volume, or incinerated before being deposited in a tip or land-fill. In many cases it is difficult to find suitable land in or near urban areas. In congested areas, the absence of the substantial areas of land required for this operation has forced the adoption of other systems.
Incineration is used successfully in several of the industrialized countries, particularly in larger cities. This method reduces the volume of domestic refuse eventually to be disposed of, usually by tipping, to about 15-20% of the original. In many older plants, however, devices for removing pollutants from the exhaust gases are inadequate to comply with present air pollution standards or those likely to be established. The increasing quantities of bulky waste such as old furniture and other household equipment, also create problems in most existing incinerators; a few installations have incorporated special equipment for breaking up such large items before incineration.
There are many ways in which components of solid waste that have some value can be recycled. But such separation of the wastes must be controlled if health hazards, degradation of the environment and impairment of disposal operations, are to be avoided. Recycling the clean, reusable portion of municipal solid waste is a favoured option for reducing the amount of waste going to landfill, and is currently attracting a lot of public attention. Estimates suggest that as much as 50% of all domestic waste could perhaps be recycled, although few are achieving even a quarter of that amount at present. Food wastes can be fed to animals; metals can be recovered and remelted, and paper can be repulped. Glass and plastics may also be removed. In some countries solid wastes have a fuel value that can be utilized. Alternately, methane gas can be withdrawn from well-engineered landfill sites and used as fuel. Composting of domestic refuse, sometimes together with sewage sludge and other organic wastes such as market refuse and agricultural waste, has been adopted in several countries. In many cases the fraction of domestic refuse that can be suitably incorporated in compost is decreasing, resulting in increasing quantities of material (up to 50% in some cases) that must be dealt with in other ways. In addition, there is some anxiety that municipal compost might have certain toxic properties, and many large composting schemes involving heavy machinery have failed because of the high cost of producing the compost, or an insufficient market.
The collection and transportation of solid wastes are very costly and may account for up to 80% of the total cost of solid wastes disposal, which in turn may absorb as much as 0.5% of the gross national product. Efficient methods are therefore vital and several unconventional systems are being developed. Current proposals for managing packaging waste in the EEC/EU favour reusable container and recycling over turning waste into energy through incineration.
In Northern Africa, at least 20 per cent and as much as 80 per cent of urban solid wastes are disposed of by dumping in open spaces. Rapid urbanization in Lagos increased solid waste generation sixfold to about 3.7 million tonnes a year in 1990, plus another half a million tonnes of largely untreated industrial waste because 90 per cent of the industries in Nigeria lack pollution control facilities (IMO 1995). The 1.3 million inhabitants of Lusaka produce 1 400 tonnes of solid waste daily, of which 90 per cent is not collected because the local authority has too few staff, funds and equipment.